Q. What cancer risks are associated with eating charcoal broiled meats? Is there a reaction between the charcoal smoke and the meat that leads to cancer? Does the risk depend on cooking temperature, cooking time or type of food?

A. There seems to be a very small cancer risk associated with years of eating a lot of smoked and charcoal cooked foods. Studies in different cultures have shown a higher risk of stomach cancer in native Japanese who eat a diet high in smoked foods, an intermediate risk in Japanese living in Hawaii where their diet is somewhere between traditional Japanese and American, and a much lower risk in Japanese who have moved to the United States and adopted a more traditional American diet with less smoked foods.

But the overall risk of stomach cancer in the United States, regardless of diet, is very low compared with other cancers that are more related to diet, life style and environment.

Some of the substances released by burning and smoking foods are known to cause cancer in laboratory animals. These substances are similar to the cancer-causing chemicals produced by burning cigarette tobacco, but not nearly as dangerous.

The very small risk from barbecued food seems to increase when food is cooked for long times at high temperatures. High-protein foods, like meat and fish, are more of a potential risk than vegetables.

You can reduce the formation of cancer-causing substances by cooking leaner meats and decreasing the amount of fat dripping on hot charcoals. Also, avoid cooking close to open flames.

But by and large I'm not saying you shouldn't enjoy a summer barbecue now and then, because eating charcoal-broiled meats doesn't seem to add significantly to the overall burden of cancer-causing factors in our environment.

Q. In your answer about benign tremor, you mentioned Parkinson's disease. Can you tell me where I can get more information on this condition? I'd like to know what causes it, how it progresses, and what the treatment is.

A. Parkinson's disease affects about half a million people in the United States, or about 1 percent of persons over 50. There are several types of Parkinson's disease, the most common one being of unknown cause. It's not hereditary or contagious.

Certain drugs, particularly antipsychotic medications used in schizophrenia, infrequently trigger a Parkinson-like condition, which usually returns to normal when the drug is stopped. Less commonly, symptoms of Parkinson's disease may follow hardening of the arteries in the brain (arteriosclerosis), multiple small strokes, or carbon monoxide poisoning.

Recently, scientists discovered that use of the illegal drug MPTP can produce a disorder indistinguishable from Parkinson's disease. Further research with the drug may turn up new methods to treat Parkinson's disease.

A part of the brain called the substantia nigra (black substance) is damaged in Parkinson's disease. This area produces a chemical called dopamine, a neutrotransmitter that stimulates certain nerve impulses in the brain. Interference with this function leads to the shaking tremor, slowness of movement, shuffling walk, expressionless face and slow speech characteristic of Parkinson's disease.

Treatment includes medications and physical therapy. The drug L-Dopa, taken orally, is converted into dopamine in the body. It helps reverse the symptoms of Parkinson's disease. Sinemet is a special formulation of L-Dopa that boosts its effectiveness. Anticholinergic medications, which influence the neutrotransmitter acetylcholine, may also help. Bromocriptine is a new medicine that has also shown promise in treating Parkinson's disease.

You can contact the following organizations for more information.

*he Parkinsonian Society of Greater Washington, 937-1545 (a local support group). This is also the number of the National Office of Parkinson Support Groups of America (literature, resources, information).

*The American Parkinson's Disease Association, 116 John St., New York, N.Y. 10038, (212) 732-9550.

Q. My 4-month-old son has a blocked tear duct in his right eye. My pediatrician recommends that I wipe the eye frequently to remove any discharge, and also gently massage the inside corner of the eye. Is there anything else I can do to clear up this problem?

A. Blocked tear ducts in infants are common, and usually short-lasting and harmless. Occasionally an infection might set in, which is usually easy to treat with antibiotics.

A tear duct is a tiny tube with one end connecting the inner corner of the eye to an opening inside the nose. Tear ducts drain the watery fluid that bathes the eye each time you blink. When you cry, tears partly drain through the tear duct into the nose, which is why the nose becomes runny.

In most infants, a blocked tear duct clears with time (usually within a few weeks to months, in some cases up to nine months) and the simple maneuver you're performing. What you're actually trying to do is massage or milk any fluid in the tear duct from its opening in the corner of the eye downward. One stroke several times a day is probably sufficient.

For persistently blocked tear ducts, an ophthalmologist can gently insert a probe into the tear duct to open it.